The present invention relates to the control of well blowouts and more particularly to a method for dynamically killing a well blowout.
Typically, wells are drilled into the earth's crust to desired subterranean locations, e.g. oil- and/or gas-bearing formations, through the application of rotary drilling techniques. In the rotary drilling of a well, a drilling mud is pumped downwardly through a rotating drill string within the well, through the drill bit at the bottom of the drill string, and thence upwardly to the surface of the well through the annulus surrounding the drill string. A "blowout" may occur when the well penetrates a high pressure gas-producing formation due to a number of circumstances. Thus, gas from a high pressure formation may enter the well and mix with the drilling mud so that its density is reduced by gas occlusion, thus reducing the hydrostatic head on the well to a value less than that of the formation pressure. A blowout may also occur during removal of the drill string from the well. Displacement of the drilling mud by the drill string may result in a decrease in the liquid level within the well with, again, a decrease in the hydrostatic head at the level of the high pressure formation.
When a blowout occurs, a number of remedial procedures are available to kill the blowout and bring the well under control. One technique involves the drilling of a relief well into a subterranean location near the blowout well. Communication between the relief well and blowout well is established and fluids then pumped down the relief well and into the blowout well in an attempt to impose a sufficient hydrostatic head to block the flow of gas from the formation into the well. Communication between the wells may be established through the high pressure sand which caused the blowout or through a separate permeable zone penetrated by both the blowout and relief wells. The formation may be acidized in order to increase the fluid conductivity between the wells. Fracturing may also be employed although in most cases this is undesirable since most fractures tend to be naturally oriented in a generally vertical direction. This is particularly true in formations at depths of about 3000 feet and more since at these depths the overburden pressure will usually exceed the horizontal stress characteristics of the formation.